The present invention relates to a detection system that detects fault currents and differential currents that are supplied to an electric device and triggers a protection switch to prevent such currents from being supplied to the electric device. More particularly, the present invention relates to a detection system that triggers the protection switch when harmful fault currents and differential currents are detected and that does not erroneously trigger the protection switch when harmless transient interference pulses are detected. In addition, the present invention relates to a method performed by the detection system and a software program for implementing the method.
In many applications, electrical currents are supplied to one or more electric devices to provide power for the devices. For example, electrical currents are supplied from a power company to one or more electrical outlets in a residential home, and a user can connect an electric device to an outlet to supply power to the device. If the electric device malfunctions or is mishandled by the user, a potentially dangerous situation may arise. For example, if the user contacts a portion of the electric device that receives electrical currents from the power company, the electrical current will pass through the user to the ground and may cause the user""s heart to suffer from a cardiac arrest. Also, if the portion of the electric device that receives electrical currents is improperly grounded due to faulty insulation, a large amount of current will be supplied to the electric device and may start a fire in the user""s home. The additional surge of current that is supplied to the user""s home when the electric device malfunctions or is mishandled is known as a fault current.
In order to prevent fire in the user""s home or to prevent the user from being harmed, a circuit breaker has been developed that detects fault currents and that blocks the supply of electrical current to the one or more electrical outlets in the user""s home if the detected fault currents exceed certain levels. FIG. 5 shows an example of such a circuit breaker 1, which comprises a sum-current transformer 2, a power supply 4, triggering circuit 5, a triggering relay 6, a switching mechanism 7, and a switch 8.
The electric currents are supplied from the power company to the user""s home via a conductor network LN, and the network LN includes three active conductors L1, L2, and L3 and a neutral or ground conductor N. The conductor network LN is wrapped around a core 3 of the sum-current transformer 2 to form a primary winding N1 of the transformer 2. Also, a secondary winding N2 is wrapped around the core 3 of the transformer 2, and the triggering circuit 5 is connected to the winding N2. Specifically, the triggering circuit 5 is connected across the output terminals of the winding N2, and the triggering relay 6 is connected across the output terminals of the circuit 5. The triggering relay 6 controls the switching mechanism 7 to selectively open the switch 8, and the switch 8 is provided in the path of the conductor network LN between the power company and the electrical device.
When the electric device in the user""s home is operating or being handled under normal conditions, no fault currents exist. As a result, the vector sum of the currents flowing through the core 3 via the conductor network LN is zero. However, if a fault current If is generated, the vector sum of the currents is not zero, and a voltage Ue is generated across the secondary winding N2. The characteristics of the voltage Ue correspond to the characteristics of the fault current If, and the triggering circuit 5 generates an output voltage Ua based on the input voltage Ue. The output voltage Ua causes an operating current Ia to flow through the triggering relay 6. When the fault current If exceeds a triggering current Itrigger, the triggering circuit 5 triggers the relay 6. The triggering of the relay 6 causes the switching mechanism 7 to open the switch 8 to block the supply of current from the power company to at least one outlet in the user""s home.
Since the value of residual operating current Ia is based on the value of the fault current If, the relay 6 triggers when the fault current If increases to a point that causes the current Ia to flow. Accordingly, when the user contacts a conductive portion of an electric device and causes a large fault current If to be generated, the relay 6 triggers, and switching mechanism 7 opens the switch 8. As a result, the dangerous fault current If is no longer supplied to the user and will not harm the user. Similarly, if the insulation in the electric device is faulty and a large fault current If is generated, the relay 6 triggers so that the switching mechanism 7 opens the switch 8. Thus, the dangerous fault current If is no longer supplied to the electric device, and any possibility of the electric device starting a fire is eliminated.
However, since the circuit breaker 1 shown in FIG. 5 is implemented via hardware circuitry, the circuit breaker 1 is often activated when dangerous fault currents are not present, and thus, the circuit breaker 1 unnecessarily interrupts the operation of the electric device. For example, when one or more electric components connected to the conductor network LN are initially turned on, transient interference pulses are generated that have large amplitudes but last for only a short period of time. For example, as shown in FIG. 1, when the electric components are turned on, transient interference pulses typically occur from the time t=0 (i.e. t0) to the time t=10 (i.e. ta, min).
When such pulses (and similar pulses) are generated, the triggering circuit 5 outputs a current Ia that triggers the relay 6, and the switching mechanism 7 causes the switch to prevent power from being supplied to the electric device. However, by the time the relay 6 triggers, the transient interference pulses no longer exist, and thus, circuit breaker 1 unnecessarily blocks the supply of the electrical power to the electric device. As a result, the operation of the electric device is unnecessarily stopped.
In an attempt to overcome the above problem, the hardware of the circuit breaker 1 has been redesigned to try to prevent it from triggering between the times to and ta, min. However, the ability to successfully redesign the circuit breaker 1 to suppress the times at which it will trigger is limited because such hardware modification is expensive and complicated. For example, the additional circuitry needed to prevent the circuit breaker 1 from triggering at certain times adversely affects the values of the triggering times at which the circuit breaker 1 needs to trigger when a fault current is detected. In addition, the time periods during which the circuit breaker 1 should trigger (or not trigger) vary based on the specific applications under which the circuit breaker 1 is to operate and vary based on the different standards adopted by different countries. Since hardware circuitry is used to control the times when the circuit breaker 1 will trigger or not trigger, modifying the circuit breaker 1 so that it can operate under different applications and according to the standards of different countries is very time consuming and difficult.
One object of the present invention is to provide a fault or differential current detection system that accurately triggers when harmful fault currents and differential currents are detected and that does not erroneously trigger when harmless transient interference pulses are detected.
Another object of the present invention is to provide a fault or differential current detection system that can be easily mass-produced and that can be easily modified to work in many different environments.
In order to achieve the above and other objects, a fault or differential current detection software program is provided. The software program is contained in a computer readable medium and includes instructions to instruct a controller to perform a routine comprising: (a) inputting a detection signal corresponding to an abnormal current generated on a conductor; (b) determining if said abnormal current is greater than or equal to a first predetermined current based on said detection signal; (c) refraining from outputting a control signal for a predetermined delay period after said abnormal current is greater than or equal to said first predetermined current; (d) determining if said abnormal current is greater than or equal to a second predetermined current after said predetermined delay period is over; (e) determining if said abnormal current is a fault current after said abnormal current is greater than or equal to said second predetermined current; and (f) when said abnormal current is said fault current, outputting said control signal at least indirectly to a switch to instruct said switch to isolate said fault current from an electric device connected to said conductor.
In order to further achieve the above and other objects, another fault current detection software program is provided. This software program is also contained in a computer readable medium and includes instructions to instruct a controller to perform a routine comprising: (a) placing said controller in a sleep mode; (b) inputting a detection signal corresponding to an abnormal current generated on a conductor; (c) determining if said abnormal current is equal to or greater than a first predetermined current based on said detection signal; (d) changing an operational mode of said controller from said sleep mode to an active mode after said abnormal current becomes greater than or equal to said first predetermined current; (e) measuring an effective value of said abnormal current after said abnormal current becomes greater than or equal to said first predetermined current; (f) refraining from outputting a control signal while said operational mode of the said controller is changing in said step (c) and said effective value is being measured in said step (e); (g) determining if said effective value of said abnormal current is greater than or equal to a second predetermined current after said effective value of said abnormal current is measured in step (e); (h) determining if said abnormal current is a fault current after said abnormal current becomes greater than or equal to said second predetermined current; and (i) when said abnormal current is said fault current, outputting said control signal at least indirectly to a switch to instruct said switch to isolate said fault current from an electric device connected to said conductor.
In order to yet further achieve the above and other objects, a fault current detection system is provided. The detection system detects a fault current generated on a conductive path supplying power to an electric device and prevents the fault current from being supplied to the electric device. The fault current detection system comprises: a detector that detects an abnormal current generated on said conductive path and outputs a corresponding detection signal; a switch that is provided in said conductive path that selectively isolates said electric device from said conductive path; and a controller that inputs said detection signal and determines if said abnormal current is greater than or equal to a first predetermined current based on said detection signal, wherein said controller refrains from outputting a control signal for a predetermined delay period after said abnormal current becomes greater than or equal to said first predetermined current, wherein said controller determines if said abnormal current is greater than or equal to a second predetermined current after said predetermined delay period is over, wherein said controller determines if said abnormal current is a fault current after said abnormal current becomes equal to or greater than said second predetermined current, and wherein, when said abnormal current is said fault current, said controller outputs said control signal at least indirectly to said switch to instruct said switch to isolate said fault current from said electric device.
In order to even further achieve the above and other objects, another fault current detection system is provided. The detection system detects a fault current generated on a conductive path supplying power to an electric device and prevents the fault current from being supplied to the electric device. The fault current detection system comprises: a detector that detects an abnormal current generated on said conductive path and outputs a corresponding detection signal; a switch that is provided in said conductive path that selectively isolates said electric device from said conductive path; and a controller that is placed in a sleep mode and inputs a detection signal corresponding to an abnormal current generated on said conductive path, wherein said controller determines if said abnormal current is greater than or equal to a first predetermined current based on said detection signal, wherein said controller changes an operational mode from said sleep mode to an active mode after said abnormal current becomes greater than or equal to said first predetermined current, wherein said controller measures an effective value of said abnormal current after said abnormal current becomes greater than or equal to said first predetermined current, wherein said controller refrains from outputting a control signal while said operational mode of the said controller is changing from said sleep mode to said active mode and while said effective value is being measured, wherein said controller determines if said effective value of said abnormal current is greater than or equal to a second predetermined current after said effective value of said abnormal current is measured, wherein said controller determines if said abnormal current is a fault current after said abnormal current becomes greater than or equal to said second predetermined current, and wherein, when said abnormal current is said fault current, said controller outputs said control signal at least indirectly to said switch to instruct said switch to isolate said fault current from an electric device connected to said conductive path.